This invention relates to methods of producing coatings on surfaces of non-metallic substrates, such as glass, to provide durable thermo-reflective coated articles.
Copper coatings have been applied by electroless plating techniques to glass and other non-metallic substrates for many years. The art of electroless plating of copper onto non-metallic substrates is characterized by a number of open literature references as well as by the following U.S. Pat. Nos.: 3,457,138 to R. G. Miller, 2,757,104 to R. B. House, 2,782,359 to E. B. Saubestre, 3,093,509 to S. Wein, 3,269,861 to F. W. Schneble et al., 3,415,666 to S. Magai et al, 3,460,952 to E. B. Saubestre et al, 3,577,273 to L. E. R. Soderburg, and 3,607,317 to F. W. Schneble.
It has been common practice to apply copper coatings from copper salt solutions, particularly cupric sulfate solutions, by employing a reducing agent, such as formaldehyde, to reduce the copper and deposit it onto a substrate. In general, the past practice has involved the use of alkaline coating solutions, with the most common alkali source being sodium hydroxide. These solutions were either sprayed or poured onto the surface to be coated or the substrate was dipped into such a solution. Contact time and solution temperature were normally the determining factors as to film thickness.
It has also been accepted practice to sensitize the non-metallic substrate to improve both the coating deposition rate and the adherence of the coating to the surface. The most commonly practiced sensitizing techniques involve an initial sensitizing step using a tin salt, particularly tin chloride, followed by a "super-sensitization" or activation step wherein a solution of noble metal salt is contacted with the surface. Palladious chloride has been found to be particularly useful for this activation step.
In general, the copper films produced by past practice are slightly pink in appearance, have excellent infrared reflectance characteristics and are sufficiently durable to be employed in architectural applications when glazed in sealed multiple glazed windows with the copper film facing the enclosed space of such units.
The films are copper metal and are generally electroconductive. Normally they will oxidize in air and will change resistivity upon being heated unless additional steps are taken to prevent this oxidation.
It has been considered a desirable objective to produce a film for architectural glasses which would be bronze, rather than slightly pink, in appearance. Elimination of oxidation and stabilization of resistivity are also considered desirable.